1. Field of the Invention
The present invention relates to an input buffer for a semiconductor memory device and, more particularly, to an input buffer for improving the noise characteristics of the memory device.
2. Discussion of Related Art
The operation of a memory device is greatly affected by various logic levels of external circuits, and external signals such as input/output impedance or noise. An input buffer utilizes and selects these external signals in accordance with the internal voltage level of the memory device. Such an input buffer should be designed to have no change of level due to noise once the logic level is defined. Additionally, the input buffer should have a voltage level as high as a logic low voltage V.sub.IL, and have a voltage level as low a as logic high voltage V.sub.IH, whereby the voltage levels are within a threshold voltage. The purpose of the above limitation in the range of the voltage level, is to enable a more rapid signal processing.
In the above described input buffer of a memory device, the output terminal is designed so as to sensitively change in accordance with the input signal level variation from HIGH to LOW or vice versa. This design is prone to cause circuit malfunctioning due to its over-sensitivity even in case of a slight change in the input signal due to noise. The input noise fed back to the output signal during reading of a data causes more problems to the memory device than writing of a data.